When implementing the rich comparison operators for some sort of container, it's tempting to save code by doing something like: class LarchTree: ... def __gt__(self, other): # A lot of code to traverse the tree def __le__(self): return not self > other However, if I'm thinking correctly, this is a bad idea. The reasoning being that > and <= are not required to be each others opposite for arbitrary value types, and may not even both be supplied by the contained objects. If a LarchTree user stores objects that don't support __gt__, will he have a legitimate complaint when using LarchTree.__le__ results in an attribute error? -- Neil Cerutti